earthquake by suman prasad mehta

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EARTHQUAKE

Suman Prasad Mehta

2008JE0319Integrated Applied Geophysics


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DEFINATION

An earthquake is a series of vibrations on the earth's

surface caused by the generation of elastic (seismic)

waves due to sudden rupture within the

earth during release of accumulated strain energy.

This only occurs where the earth is solid and therefore

can only occur within about 100 miles of the surface


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CAUSES OF EARTHQUAKE

Motion of the continental crust.Faulting may be considered as an immediate cause ofan earthquake.Due to constant movement of plates, deformation iscaused which results to generations of strain energy.

Example : Indian plate is moving in north-north-east direction and colliding with Eurasian plate alongthe Himalayas.


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TERMINOLOGY

The hypocenter is the point within the earth

where an earthquake rupture starts.

Also commonly termed the focus.

HYPOCENTER

EPICENTER

The epicenter is the point on the earth's surface

vertically above the hypocenter (or focus), point in

the crust where a seismic rupture begins.


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TERMS RELATED TO EARTHQUAKE


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SEISMIC WAVES

A seismic wave is an elastic wave generated by an impulse such as an

earthquake or an explosion.

TYPES OF SEISMIC WAVES

- BODY WAVES

P and S

- SURFACE WAVES

R and L


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BODY WAVES

A body wave is a seismic wave that moves through the interior of the earth,as opposed to surface waves that travel near the earth's surface.

P or primary waves

fastest wavestravel through solids, liquids, or gasescompressional wave, material movement is inthe same direction as wave movement

S or secondary waves

slower than P waves travel through solids only shear waves - move material perpendicular

to wave movement


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PROPAGATION OF :-

PRIMARY WAVES SECONDARY WAVES


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SURFACE WAVES : R AND L

A surface wave is a seismic wave that is trapped near the surface of the

earth.

Travels just below or along the grounds surface

Slower than body waves; rolling and side-to-side movement

Especially damaging to buildings
http://earthquake.usgs.gov/learning/glossary.php?termID=178http://earthquake.usgs.gov/learning/glossary.php?termID=178


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SEISMOGRAPH

A seismograph, or seismometer, is an instrument used to detect and record the

vibration and disturbance in the earth crust ,that may be an earthquakes

It consists of a mass attached to a fixed

base.During an earthquake, the base moves

and the mass does not.

The motion of the base with respect to

the mass is commonly transformed into

an electrical voltage.

The electrical voltage is recorded onpaper, magnetic tape, or another

recording medium


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HOW IS AN EARTHQUAKES EPICENTER LOCATED?

Seismic wave behavior

P waves arrive first, then S waves, then L and R Average speeds for all these waves is known

After an earthquake, the difference in arrival times at aseismograph station can be used to calculate the distancefrom the seismograph to the epicenter.


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Time-distance graphshowing the averagetravel times for P- and S-waves.

The farther away aseismograph is from thefocus of an earthquake,the longer the intervalbetween the arrivals ofthe P- and S- waves


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Three seismograph stationsare needed to locate theepicenter of an earthquake

A circle where the radius

equals the distance to theepicenter is drawn

The intersection of thecircles locates theepicenter


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INTENSITY OF AN EARTHQUAKE

It is the rating of the effect of an earthquake at a particular place, basedon the observations of the damaged areasIt describes the severity of an earthquake in terms of its effects on

the earth's surface and on humans and their structures.

Giuseppe Mercalli

1850 - 1914

Giuseppe Mercalli , an Italian volcanologist

developed the MercalliIntensity Scale.

This scale measures the intensity of shaking with

numbers from I to XII


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Amplitude of the largestwave produced by an eventis corrected for distanceand assigned a value on anopen-ended logarithmicscale

First a seismograph is obtainedfrom the seismic station .


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FEATURES OF THE TWO SCALE


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SOME IMPORTANT EARTHQUAKE IN INDIA

BHUJ , 2001

Date : 26th January ,2001

Magnitude : 7.7

Depth : 16 kilometer

Epicenter : 23.442N 70.310E

Casualties : 19,727 dead, 166,000

injured .

This was one of the biggest earthquake in the history of India and itOccurred due to the relative motion between the Eurasian plate and Indianplates.
http://stable.toolserver.org/geohack/geohack.php?pagename=2001_Gujarat_earthquake&params=23.442_N_70.310_E_http://stable.toolserver.org/geohack/geohack.php?pagename=2001_Gujarat_earthquake&params=23.442_N_70.310_E_http://stable.toolserver.org/geohack/geohack.php?pagename=2001_Gujarat_earthquake&params=23.442_N_70.310_E_http://stable.toolserver.org/geohack/geohack.php?pagename=2001_Gujarat_earthquake&params=23.442_N_70.310_E_http://stable.toolserver.org/geohack/geohack.php?pagename=2001_Gujarat_earthquake&params=23.442_N_70.310_E_http://stable.toolserver.org/geohack/geohack.php?pagename=2001_Gujarat_earthquake&params=23.442_N_70.310_E_


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Jabalpur 1997

Date : 22nd May,1997

Magnitude : 6.0

Depth : 35 kilometer

Epicenter : 23.18 N , 80.02 E

Casualties : 39 dead,

Latur 1993

The Latur (Killari), Maharashtra, earthquake of September 30, 1993

Its epicentre was located in a region considered to be aseismic.

magnitude 6.3 and focal depth less than 10 km


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WORLD SEISMIC ZONE


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EPICENTERS LOCATION


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SEISMIC ZONE OF INDIA


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NETWORK OF SEISMOLOGICAL OBSERVATORIES IN INDIA


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REFERENCES

ELEMENTARY SEISMOLOGY by Charles F. Richter

http://earthquake.usgs.gov/

http://www.iris.edu/USArray

http://bssaonline.org


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earthquake by suman prasad mehta

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